Prostate cancer is the leading cause of cancer-related death in men in the United States, but there is no effective treatment for patients who develop recurrent disease after surgery or radiation therapy or those who have metastatic disease at the time of diagnosis. Thus, the development of effective immunotherapy is important for patients with prostate cancer. However, a lack of knowledge of MHC class I- and II-restricted prostate cancer antigens is a major hurdle for developing effective immunotherapy of prostate cancer. In the last few years, significant progress has been made in defining several classes of tumor antigens from melanoma as well as other cancers, which led to clinical trials. These studies hold the promise of effective treatment of patients with cancer. The objective of this application is to identify MHC class I- and II-restricted prostate cancer antigens as immune targets and to develop effective cancer vaccines for the therapeutic treatment of patients with prostate cancer. The rationale for the proposed research is that CD4+ T (helper) cells orchestrate and amplify immune responses by providing critical help for priming, activation and proliferation of CD8+ T cells. The expansion of tumor-specific CD4+ as well as CD8+ T cells will lead to tumor regression. Our recent studies showed that NY-ESO-1 is an immunogenic cancer antigen containing both MHC class I- and II-restricted peptides, and is expressed in 20-25 percent of prostate cancer samples. We hypothesize that MHC class 1- and II-restricted tumor specific peptides are presented on the prostate cancer cell surface for T cell recognition; Vaccination with MHC class I- and II-restricted NY-ESO-1 and other new antigens we intend to identify will directly activate tumor specific CD4+ T cells and CD8+ T cells, resulting in potent antitumor immunity. Since we have developed novel technologies for identifying both MHC class I- and II-restricted tumor antigens and established important reagents, we are well prepared to define these new immune targets. We will then evaluate and improve the immunogenicity of T-cell peptides derived from NY-ESO-1 and new prostate cancer antigens for vaccination, and assess the role of T cell responses in preclinical tumor models. With all information and reagents at hand, we will evaluate antitumor immune responses in human clinical trials by incorporating both MHC class I- and II-restricted peptides in cancer vaccines.